Figure 2.

The auxin pathway is affected by the presence and quality of light. (A) Light stimulation reduces sensitivity to auxin. Activated phytochrome promotes the accumulation of auxin transcriptional repressors. Repression of degradation machinery, including the COP9 signalosome, results in stabilization of transcription factors such as HY5. (B) In the dark, active degradation of light transcription factors results in reduced accumulation of auxin transcriptional repressors and high auxin sensitivity. (C) In shaded conditions or close proximity to a neighboring plant, increased auxin biosynthesis and transport result in an increased transcriptional response that contributes to the shade avoidance syndrome. Dotted lines indicate decreased levels of proteins or complexes.